The Moon is important and unique for many reasons. The Moon is huge for one. Proportional to the Earth, the Moon is far larger than any other satellite in the Solar System, with the exception of Pluto's moon Charon, but Pluto isn't much of a planet. This means that the Earth gets phenomenon like tides and visible phases of the moon. If the moon had proportionally the size of say, Mars' moons, then we would see neither of these, and they are both important.

The tides the Moon created may have played a role in getting life to move out of the oceans, since some animals would be trapped in the intertidal zone and adapted to being out of water for a period of time.

The Moon has played a very important role in the development of astronomy, which is the oldest science known to man because the first astronomical observations were the phases of the Moon which have occurred for all of recorded history. The Moon is the basis for many calendars, including ours.

The Moon

I wrote this on the train trip from London back to Chorley via Manchester Piccadilly. I was totally captivated by her and forgot how long it had been since we last saw each other.. Also thanks The Alchemist for spotting the typo in the 3rd verse. :)

i) The effect of the gravitational attraction of the Earth on the moon is far smaller than the effect of the gravitational attraction of the Sun on the moon. The Earth and the Moon are more accurately described as double planets circling the sun.
- if either the Earth were to suddenly disappear, the Moon would keep on orbiting around the Sun. On the other hand, if Jupiter were to suddenly disappear, its moons would go flying in every direction.

ii) The moon orbits the Earth in a plane aligned with the other planets of the solar system, rather than in an equatorial plane of the Earth, which would tend to be the case with traditional satellites.

So the take home message is that The Moon is not a moon! (but rather the Earth's partner in a double planet system)

Analysis of data from the Lunar Prospectorspacecraft in 1999backs the long existing theory that the Moon masses were ripped away from young Earth when an object the size of Mars ran into it. Parallels in the mineral composition of Earth and the Moon hint at a commonorigin. This similarity was already known. In the past, some scientists have translated this into an indication that Earth and the Moon had formed separately from the same cloud of rocks and dust.

The recent Lunar Prospector data shows however that the Moon has a smallcore that contains less than 4% of the Moon's total mass. Earth's iron core contains approximately 30% of the planet's mass. If Earth and the Moon had merely formed from the same blur of rocks and dust, the Moon would have a core comparable in proportion to Earth's, scientists claim. A much more liablethought is that a large body struck Earth, forcing a release of rocky matter from the outer shell into orbit, which collected to form the Moon.

The answer: Not a damn thing. The best I can do for you here is share these (rather unpoetic) facts.

The moon is earth's only naturalsatellite, and one of the few objects in the sky that you can see with a fair amount of detail. (The other is the sun. I wouldn't recommend looking for details on the sun however.) It is our closest neighbor in the universe, and the only other celestial body upon which human beings have walked. (For the purposes of this write-up, I'm going to assume that man has, in fact, walked on the moon, and that it wasn't an elaborate hoax).

At the time of this writing (and for the foreseeable future) only 12 human beings have had the privilege of walking on the moon.

Note the conspicuous absence of Apollo 13. Apollo 13 was not skipped, like the thirteenth floor of a building is skipped. Indeed, Apollo 13 was launched on 11 April 1970, but unfortunately it never made its way to the moon. You can read about that ill-fated mission elsewhere.

But I want to walk on the moon!

Okay, let's say that you were to walk on the moon. One of the first things you would notice, right after you realize that you are currently 238,866 miles (384,400 kilometers) from the nearest pay-toilet, and the horizon is significantly closer than what you're used to, is that your weight has dropped to 1/6 of its earth-weight. (Your mass, quite predictably, does not change, so you will not need smaller pants.) The gravitational pull of the moon is significantly less than that of earth, and for a human body which has evolved a system of muscles adapted to earth's gravitational pull, you can jump and throw objects with superhuman effects.

The next thing you would probably notice is that you are standing ankle deep in some sort of dusty crap. The dust is called regolith. Regolith is a rocky/dusty mixture which is produced by meteorimpacts. With no atmosphere (and no cleaning staff), the dust from such impacts lays where it falls. Also, because of the lack of atmosphere, meteors do not burn in the sky like they do on earth, and surface strikes occur much more easily, and frequently. Because of those two conditions, most of the entire moon's surface is covered in craters and regolith.

So, you've spent most of the day walking around on the moon (and you're amazed that your legs are not tired yet), and now you're waiting for the earth to go down, so you could enjoy a lovely "earthset", perhaps with tea and biscuits. You are going to be waiting for a very long time. You've perhaps noticed that the same side of the moon always faces the earth. This is because the moon rotates synchronously in relation to earth. It's rotation is phase-locked with its orbit around the earth. This is because of the tidal pull of the earth on the moon. This phenomenon can be seen among most satellites in the solar system. (Pluto, however, is the only planet that also is in synchronous rotation to its moon, Charon). Since our moon is so large in proportion with the earth, it's exerting its own tidal pull - witness the tides of the ocean. This pull is doing the the same thing to earth that the earth has done to the moon, but much more gradually. The tides are slowing the earth's rotation so that eventually, earth will be locked in synchronous rotation with the moon. However, the moon does wobble a bit, because its orbit is elliptical. Because of the wobble, you can get a small (very small - only a degree or two) glimpse of the dark side occasionally.

Because of the "closeness" in size between the earth and the moon, they are sometimes referred to as double planet. The moon does not orbit the earth as such, but rather, they both rotate around a center of mass, or a barycenter, like an unbalanced dumb-bell. The barycenter is actually about 1,000 miles under the surface of the earth, so we usually just say the moon orbits the earth.

One of the less remarkable things you'd notice during your walk around the moon is that your compass doesn't work. The moon has no magnetic field. Luckily there are no woods in which you can get lost.

Okay, I'll just admire it from here

From earth, the most notable aspect of the moon is the fact that it goes through phases during its orbit. The phases exist because varying amounts of the visible surface of the moon are illuminated by the sun during its orbit. The new moon occurs when the side of the moon facing the earth is not illuminated at all, and the full moon occurs when it's completely bathed in sunlight. Other phases include the gibbous moon where the moon's earth-face is mostly lit, and the crescent moon where it is slightly lit. Then, of course, there is the half-moon when (duh) half the moon is illuminated.

Another noticeable aspect of the moon from earth are the craters and mountains and plains (oh, my). The craters, as stated above, were made by meteor collisions. The plains are called maria (seas), so called because they were once thought to be bodies of water. The maria appear to be darker than the rest of the moon. That's because they are darker than the rest of the moon. They are darker because they were craters which filled with the moon's volcanic lava after particularly nasty meteor strikes. The maria are what create the man in the moon image. Space photos show that there are no maria on the dark side of the moon, although the entire hemisphere is pockmarked and cratered.

The moon is also the cause of a phenomenon known as an eclipse. A solar eclipse is when the moon passes between the earth and the sun. Because of a strange unique quirk in nature, the moon is just the right distance away from the earth to appear exactly the same size as the sun. Because of this we get a bonus light show during a total eclipse. That bonus is that the surface of the sun is blocked out, but the corona of the sun is still very visible, (visible enough to burn out your retinae) and during those rare total eclipses it appears as if the sun is black but still shines. If you want to view a total eclipse, you can buy a special box which dims the light to a sufficiently non-blinding magnitude.

Lunar Eclipses occur when the earth gets between the sun and the moon. You may guess that there is no such quirk that makes the earth appear the same size as the sun, and during a total lunar eclipse, the whole sun gets blocked and the moon goes black, or at least very dark. A total lunar eclipse is when the moon enters the umbra of the earth - or the darkest shadow of the earth, and a partial lunar eclipse is when the moon enters the penumbra, which makes the moon appear a reddish color. In the book of Revelation in the Christian Bible there is a reference to the moon turning to blood. This is most likely a prophecy that there will be a partial lunar eclipse in the end times which makes the moon appear blood red.

So, where did it come from?

There are a few theories on the moon's origin. One of the leading theories is that the moon was formed as a result of an enormous terrestrialcollision. A large body - perhaps even the size of Mars - skipped off the earth sending debris into space, which eventually accumulated into a central mass. (I don't really buy that one, but what the hell do I know?) Another theory is that the moon was formed at the same time and in conjunction with the earth's formation.

Been there, done that

The United States and The Soviet Union spent much of the sixties engaged in a space race, to see who could reach the moon first. The US won in 1969 with the touchdown of Apollo 11, and a mere three years later, that was it. No more moon trips. In fact, if we wanted to send someone to the moon right now, we couldn't do it. We are currently unequipped to send someone there. Oh, sure, we have the technology to build the things necessary to go, but that's the thing, we'd have to build it all. So, it seems that the moon will remain unmolested for a while.

One of the reasons I've seen cited for the fact that noone's gone to the moon in almost 3 decades is because there is no money in it. Mining for resources on the moon would be ludicrous because everything we need can be so cheaply obtained here. Any research that would be done on the moon wouldn't be beneficial, or the cost would outweigh the benefit. (Any stories you've heard about Coca-Cola or Nike shining their logo on the moon are mere urban legends- and not even good ones).

But I think I've discovered a plan on paying for it. Let the Fox network pay for it. Who would not watch the reality show, Survivor, if it was set on the moon? With the proper hype, that could be the most lucrative ventures in broadcast history!

In days gone by there was a land where the nights were always dark,
and the sky spread over it like a black cloth, for there the moon
never rose, and no star shone in the gloom. At the creation of
the world, the light at night had been sufficient. Three young
fellows once went out of this country on a travelling expedition,
and arrived in another kingdom, where, in the evening when the sun
had disappeared behind the mountains, a shining globe was placed
on an oak-tree, which shed a soft light far and wide. By means
of this, everything could very well be seen and distinguished,
even though it was not so brilliant as the sun. The travellers
stopped and
asked a countryman who was driving past with his cart, what kind
of a light that was. "That is the moon," answered he, "our mayor
bought it for three talers, and fastened it to the oak-tree. He
has to pour oil into it daily, and to keep it clean, so that it
may always burn clearly. He receives a taler a week from us
for doing it."

When the countryman had driven away, one of them said, "We could
make some use of this lamp, we have an oak-tree at home, which is
just as big as this, and we could hang it on that. What a
pleasure it would be not to have to feel about at night in the
darkness.""I'll tell you what we'll do," said the second, "we will
fetch a cart and horses and carry away the moon. The people here
may buy themselves another." "
I'm a good climber," said the third, "I
will bring it down." The fourth brought a cart and horses, and the
third climbed the tree, bored a hole in the moon, passed a rope
through it, and let it down. When the shining ball lay in the
cart, they covered it over with a cloth, that no one might observe
the theft. They conveyed it safely into their own country, and
placed it on a high oak. Old and young rejoiced, when the new
lamp let its light shine over the whole land, and bedrooms and
sitting-rooms were filled with it. The dwarfs came forth from
their caves in the rocks, and the tiny elves in their little red
coats danced in rings on the meadows.

The four took care that the moon was provided with oil, cleaned
the wick, and received their weekly taler, but they became old
men, and when one of them grew ill, and saw that he was about to
die, he appointed that one quarter of the moon, should, as his
property, be laid in the grave with him. When he died, the mayor
climbed up the tree, and cut off a quarter with the hedge-shears,
and this was placed in his coffin. The light of the moon
decreased, but still not visibly. When the second died, the
second quarter was buried with him, and the light diminished. It
grew weaker still after the death of the third, who likewise took
his part of it away with him, and when the fourth was borne to his
grave, the old state of darkness recommenced, and whenever the
people went out at night without their lanterns they knocked
their heads together in collision.
When, however, the pieces of the moon had united themselves
together again in the world below, where darkness had always
prevailed, it came to pass that the dead became restless and awoke
from their sleep. They were astonished when they were able to
see again, the moonlight was quite sufficient for them, for their
eyes had become so weak that they could not have borne the
brilliance of the sun. They rose up and were merry, and fell
into their former ways of living. Some of them went to the play
and to dance, others hastened to the public houses, where they
asked for wine, got drunk, brawled, quarreled, and at last took
up cudgels, and belaboured each other. The noise became greater and
greater, and at last reached even to heaven.
St. Peter, who guards the gate of heaven, thought the lower world
had broken out in revolt and gathered together the heavenly hosts,
which were employed to drive back the evil one when he and his
associates storm the abode of the blessed. As these, however,
did not come, he got on his horse and rode through the gate of
heaven, down into the world below. There he reduced the dead to
subjection, bade them lie down in their graves again, took the
moon away with him, and hung it up in heaven.

Fission: the Moon was torn out of the Earth at some early stage of its evolution by unknown but tremendous forces.

The first two theories were dismissed during the early phases of lunar exploration, when it became known that the oxygen isotopic ratios of lunar rocks were virtually identical to that of the Earth's mantle. The final theory, that of fission, came into focus as being the most likely. However, even this had flaws.

The Earth has a large iron core, whilst the Moon has none. In addition, the mean density of the Earth is higher than that of the Moon.

A refinement of the fission theory was developed. Currently it states that the Moon formed from a collision with the Earth in a fairly late stage of the Earth's development.

A roughly Mars-sized protoplanet collides with the protoEarth at a near-zero relative velocity. The mantle of the Earth is shattered at the point of contact, and debris is ejected into orbit around the damaged planet: since the iron core of the Earth has already formed at this stage, none of this material is contained in the ejecta.

The ejected mantle material coalesces into a single body, the Moon, which achieves a stable orbit around the Earth. This results in an Earth with a still-preserved iron core, and mantle containing original and impact material as well as a Moon which has a) a similar mantle composition to Earth and b) no iron core, which accounts for the lower overall density of the satellite.

The gravitational force between the earth and the mood causes both objects to bulge towards each other slightly.
This is the tidal force. The earth is rotating and this rotation causes the bulge to move ahead, slightly, of the line between the centre of the earth and the centre of the moon!, this disrupts the isotropic gravitational field and produces a slight torque on the moon. In this way the rotation of the earth an the orbit of the moon are coupled. The earth's roatation slows down slightly and the moon's orbital velocity gets a litte bigger. The orbit of a body is directly connected to its orbital velocity, hey presto the moon, as it speeds up in its rotation, moves slightly further away from the earth.

The reason that the moon is locked into an orbit in which the same face is presented to the earth as it roatates about the earth is due to this same reason. The moons rotational engergy, through this coupling, settled into this state.

A consequence, as the moon moves away from the earth a total eclipse of the sun will no longer be possible, so catch one while you still can! (It will take a humanly relativly long time before total eclipses stop happening.)

One widespread misconception about the Moon is that it does not have an atmosphere. In fact, it does have an atmosphere, it's just that it has no atmosphere to speak of; it has a mass of less than 50 metric tons, and is spread over a surface area the size of Africa. To give you an idea of just how insignificant that is, a paper published in 1974 estimated that each Apollo mission actually temporarily doubled the size of the Moon's atmosphere1. The reason for the Moon's smoke wisp of an atmosphere is that the sun constantly bombards the solar system with solar winds and ultraviolet light, which ionize gas atoms on contact; this ionization in turn subjects these atoms to the mercy of interplanetary magnetic fields, which send them sailing off into the void (this effect is the basis of the ion propulsion drive, which is far more effective and provides more total velocity than rocket engines.)

In paper cited above, the author also estimated that the creation of an earth-density atmosphere on the Moon could be accomplished by vaporizing oxygen-rich moon dirt with nuclear blasts. Not only is this idea bat-out-of-hell crazy, it would require a nuclear arsenal 10,000 times the size of the U.S.'s current one, the creation of which would be both technologically and politically prohibitive.

Another important aspect of the Moon is that its influence keeps the Earth from wobbling around on its axis, which is set at a very specific 23.5 degrees. It is this orientation that keeps weather patterns stable, i.e. winter during one part of the year and summer during another. If the Moon were magically removed, the Earth could wobble around wildly, causing ice to form where jungles once bloomed and life in general to change beyond all recognition.

1 "Creation of an Artificial Lunar Atmosphere," Richard R. Vondrak, Nature, Vol. 248, April 19, 1974, pp. 657-659-- I found this on a website called MarsInstitute.info, a wonderful little site that has summarised and cataloged hundreds of papers about potential missions to Mars and the Moon. Unfortunately, sporadic interest in space exploration has prevented any of these ideas from coming to fruition

As you can see from the other write-ups here, there is a lot to say about The Moon. It is only right that scientists, poets, historians and mystics all have an intimate understanding of it, as it is, in a sense, the property of us all, even if it is just as an enigma to wonder upon.

There is one basic understanding of the moon that I have never yet seen written down, and am continually surprised at how few people know it, even to the the extent that a popular piece of moon phase software got it wrong, despite the arcane detail it contained. The observation is simple, it is one that our forebears would all have known immediately, almost instinctively, perhaps we have lost it because we habitually gain our knowledge without looking at the subject itself, that and the fact that the moon no longer plays a role in ordering our schedules as it once did*.

The simple observation is this:
The waxing moon has its convex curve to the right hand side (the chunk is missing from the left hand side), till it grows full round, then as it wanes the curve is on the left (the chunk missing from the right), till it becomes new (at its darkest). In other words only the waning moon is a C.
Not very important maybe? But next time you see the moon you will be able to tell if the nights are getting brighter or duller, something that up until living memory any small child would have known. Try asking your friends if they know the difference.

Thanks to DonJaime who has pointed out that in the southern hemisphere it's the other way round. Having never been, I cannot confirm this, I would be grateful if anybody else could confirm it as so.

*Before streetlights and automobiles, journeys were planned to make the most of the full moon to light the way, the great historic balls and other great gatherings were scheduled to correspond with the full moon to minimise the risk to those invited. During the new moon social calendars for large groups were restricted to the daytime, the roads would have been comparatively empty at night except for those who did not have to travel far, or who had no alternative.